Very Large Telescope

The world's most advanced visible-light astronomical observatory

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The Very Large Telescope array (VLT) is the flagship facility for European ground-based astronomy at the beginning of the third Millennium. It is the world's most advanced optical instrument, consisting of four Unit Telescopes with main mirrors of 8.2m diameter and four movable 1.8m diameter Auxiliary Telescopes. The telescopes can work together, to form a giant ‘interferometer’, the ESO Very Large Telescope Interferometer, allowing astronomers to see details up to 25 times finer than with the individual telescopes. The light beams are combined in the VLTI using a complex system of mirrors in underground tunnels where the light paths must be kept equal to distances less than 1/1000 mm over a hundred metres. With this kind of precision the VLTI can reconstruct images with an angular resolution of milliarcseconds, equivalent to distinguishing the two headlights of a car at the distance of the Moon.

The 8.2m diameter Unit Telescopes can also be used individually. With one such telescope, images of celestial objects as faint as magnitude 30 can be obtained in a one-hour exposure. This corresponds to seeing objects that are four billion (four thousand million) times fainter than what can be seen with the unaided eye.

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On extremely clear days the magnificent 6739-metre volcano Llullaillaco is visible in the background of this photograph. It is an amazing 190 kilometres away on the border with Argentina. (09 Mar 2017 19:01 CET)

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Telescopes and Instruments

The VLT instrumentation programme is the most ambitious programme ever conceived for a single observatory. It includes large-field imagers, adaptive optics corrected cameras and spectrographs, as well as high-resolution and multi-object spectrographs and covers a broad spectral region, from deep ultraviolet (300 nm) to mid-infrared (24 µm) wavelengths.

The Unit Telescopes

The 8.2m diameter telescopes are housed in compact, thermally controlled buildings, which rotate synchronously with the telescopes. This design minimises any adverse effects on the observing conditions, for instance from air turbulence in the telescope tube, which might otherwise occur due to variations in the temperature and wind flow. The first of the Unit Telescopes, 'Antu', went into routine scientific operations on 1 April 1999. Today, all four Unit Telescopes and all four Auxiliary Telescopes are operational.

The Auxiliary Telescopes

Although the four 8.2-metre Unit Telescopes can be combined in the VLTI, they are mostly used for individual observations and are only available for interferometric observations for a limited number of nights every year. But four smaller, dedicated 1.8-metre Auxiliary Telescopes (ATs) are available to allow the VLTI to operate every night.

Science with the Very Large Telescope

The VLT has made an undisputed impact on observational astronomy. It is the most productive individual ground-based facility, and results from the VLT have led to the publication of an average of more than one peer-reviewed scientific paper per day. VLT contributes greatly to making ESO the most productive ground-based observatory in the world. The VLT has stimulated a new age of discoveries, with several notable scientific firsts, including the first image of an extrasolar planet (eso0428), tracking individual stars moving around the supermassive black hole at the centre of the Milky Way (eso0846), and observing the afterglow of the furthest known Gamma-Ray Burst.

Did you know?
The smallest detail distinguishable with the VLT's adaptive optics system is smaller than the size of a DVD on the International Space Station, as seen from the ground (about 50 milliarcseconds)

Did you know?The smallest detail distinguishable with the VLT's adaptive optics system is smaller than the size of a DVD on the International Space Station, as seen from the ground (about 50 milliarcseconds).

Did you know?The smallest detail distinguishable with the VLTI is about the size of a sesame seed on the International Space Station, as seen from the ground (about 2 milliarcseconds).

Did you know?Stars form in dense clouds of the interstellar medium, but even in these densest regions the pressure is comparable to the most tenuous vacuum created in a laboratory on Earth. In these clouds, the temperatures are below -200 degrees Celsius.

Did you know?When astronomers combine the light waves from two telescopes using the principle of interferometry, they can very precisely determine the direction of an object in space. Your ears work in a similar way to localise sounds, by comparing the sound received at the left and right ears.

Did you know?The skies over the ESO sites in Chile are so dark that on a clear moonless night it is possible to see your shadow cast by the light of the Milky Way alone.

Did you know?The VLT 8.2-metre diameter primary mirrors were polished so precisely that if they were scaled up to the diameter of the Earth, the largest imperfection on them would still be no larger than a pebble.

Did you know?The VLT mirrors are 8.2 metres in diameter, but only 17.5 cm thick — very thin relative to their size. If you scaled the mirror down to the size of a CD, its thickness would be equivalent to just two discs placed on top of each other. Despite being very thin, the large diameter means the glass weighs 23 tonnes.

Did you know?The movable structure of each VLT Unit Telescopes weighs about the same as a fully loaded jumbo jet. However, it is so perfectly balanced, resting on hydrostatic oil-film bearings, that the giant telescopes can be moved by hand.

Did you know?The Paranal observatory site is so remote that everything needed must be brought in specially. The 60 000 litres of water that are used per day are delivered by truck from Antofagasta.